Balanced mixer



H. J. RIBLET BALANCED MIXER Sept. 18, 1951 5 Sheets-Sheet l Filed June 22, 1948 H. J. RIBLET BALANCED MIXER Sept. 1S, 1951 5 Sheets-Sheet 2 Filed June 22, 1948 mm u ww m mw H. J, RIBLET BALANCED MIXER Sept. 18, 1951 5 Sheets-Sheet 3 Filed June 22, 1948 /A/l/E/VTOR HENRY J, F/BLET Sept. 18, 1951 H, J, RIBLET 2,568,090

BALANCED MIXER Filed June 22, 1948 5 *Sheets-Sheet 5 Patented Sept. 18, 1951 -nNrTE-D BALANCEDMIXER Henry J. Riblet, 'Be1m0nt,. Mass., assignor to Raytheon Manufacturing Company, a; corpura- 'tion of Delaware rApplcationJune'ZZ, 1948, Serial No. 34,536

(Cl.'f250-2`0) "15 Claims. .-.1

I.This invention relatesgenerally to mixing .cir- .cuits 7for-radio receivers, .and .in .particular toa ==novelmixer circuit.. employing direction-al. coulplers for= independentlyY mixing an incoming radio Y.frequency .signaland. an automatic frequency #control signalA with the. same. local oscillator nvoltage.

...In radarsystems. ,particularly those operating in the microwave range, itiscuStOmary to employ a superheterodyne receiverwherein the received signal is. mixed with alocal oscillator sig- ..nal, and the mixed signals are then passed into ...an intermediate .frequency amplifier where .the first .amplification takes. place. The I.' amplifier has a denite band width, which necessitates -that-the local oscillator frequency shall be accurately controlled. It is, therefore, alsonow' the practice to compare the transmitter oscillator frequency withthe, local oscillatorfrequency and ,to provide means to. maintain'. av constant. vdifference between them, namely, a diieren'ceithat is related tc the intermediate frequency. This is laccomplished by mixing. a sample of 'the transmitted signal voltage with the 'local oscillator voltage, and feeding the resultant'difference sig- ..nal into an automatic:I frequency control-circuit which .functions to tune'the local oscillatorto vfmaintain the diierence signalfrequency "con- ='stant. YThe use of directional 'couplers'in radar systems to prov-ide suchcircuitsis-,described in a paper entitled Directive Couplers in Wave u V4(.`uides, by Surdin, published' in vthe `Journal -of the Institution of-Ele^ctrical -Engineers, Lonfdon, England, vol.- 93, part IIIA-Nor 4, 1-946, 'pages `v` 1725 to "736; vatpage725.

vThe present finventicn'has Ias kits main. object to provide an improved i :balanced :mixer circuit employing i .directional couplers; characterizedsby ifcompaotness and broad band width.

'It is.an`other object. toprovide suchianlim- .ff-proved directional coupler "circuit which .inde- ...pendently .mixes local';oscillator;vo1tagef .with:;in coming signal voltage `fromiathe :.antennaand '-fzwith' automatic vfrequency .1 control i Voltage from the transmitter.

= Ilt'f'is .another` object of @thev invention to provide such a circuitwhich functions as a -balanced mixer, andsupplies twooutputwvoltages foreach i' voltage that is vmixed with the zlocal oscillator vvvoltage, the two voltages being at-equal power levels. It .is another object of. Vthe l invention yto provide-such a balancedmixer` circuit wherein the two voltages are. suitablyphased. .for direct ...use in push-pull amplication.

It is a further vobject of..tllednventionfto .pro- .vide suchl a .circuit whichmas broad-band char- ."Fig.'..2 isa cross-sectional view on line 2-4-2'of Fig. 1;

Eigf 3 is a .side-'sectional View on line' 33"`of .Figi 2;

'Fig. 4 is V a 'top-sectional viewon line 4-14 of .lig 5'is a flow Vdiagram .illustrating the operation 'of 'theinventon l"Fig," 6"is.a;diagram*for aid in understanding theoperation oflthe' invention;

.Fi'gs. 'lfto"'10,"'inclusive, are vector diagrams 'illustrating the-operation' of 'the invention;

Fig. 11"'is a'modulatiomenvelope diagram-illus- 'Jtratingthe operation of the invention;

"`l." ig.' -'12: Ais"'a-"vector diagram illustrating-Whe 'operation'ofitl'ie'invention;` and wFigi13iillu'stra-tes` the'connection ofthe circuit vv'of ltheinvention to the lpusl'i-pull amplier.

"Referring now-tor Figs.4 1' to- 4, inclusive,'i'our substantially *identical rectangular waveguides `rl l, 12H3, a-r1d"=|i=are .disposed paralleli to `each Mother; eachfwith'a narrow wall adjacent to that fof-1 a' neighbor 'andl a -wide wall adjacent -toLthat *ofy aedinerent bneighbor. i .In lithe .preferred form l"oi-1constructionpas shown in Fig. .2, .the instand ffsecoridiwaveguides' 'I and il2isharev a first-*com- 'rm'on anarrowfvzall AI 5,.the secondand third guides ifi Zand i13.?sharealfirstzcommon-wide wall |.6,:the '..ithirdfand :fourthzguides l3-.and I4 shareafse'cond .fecomm'oninarrowiwall |1,. and' .the` fourtmand 'iiirstguides-@Iil` and Il share a secondrcommon r -.together through. the rst common-widewall ,Hi

by'wayaoba seconddirectional coupler'C, oa lkind which .iscdescribed `indetail .and `claimed in rcopending application, `Serial'l No. Y784,277,fliled November 5, y1947. `This coupler comprises a pluralityof transversely. directed'slots '.'225 'c'enteredsubstanuany along thev center' une ofthe wall in which they are cut, and a plurality of longitudinally directed slots 23 disposed near the edges of the wall, as shown clearly in Fig, 4. The rst and fourth waveguides II and I4 are similarly coupled together through the second common wide wall I8 by way of a third directional coupler B, which is identical to directional coupler C.Y It will be recognized by those skilled in the art that the slots of directional coupler A are so directed that they are perpendicular to the current now in the rst common narrow wall I of power in fundamental, or TEo,1 mode, and are, therefore, advantageously disposed to be excited by current of this mode. L Directional cou-` plers B and C are likewise intended for use with the fundamental mode, as is explained in said copending application.

Each directional coupler is dimensioned to function as a hybrid; that is, the coupling ratio issubstantially unity, so that it couples substantially one half of the power presented to it. To this end the slots of each coupler are made nonresonant to waves at the operative frequency,

Aso thateachv slot couples only a small amount of the power presented to it, and the number of slots of -each coupleris then chosen to effect a coupling ratio of unity. lWith respect to couplers B and C, this construction is explained in detail in the aforementioned copending application, where the form of coupler in which the coupling ratio is unity is referred to as a bridge circuit.

-Couplers B and C are of the species illustrated in Fig. 1l of said copending application, in order that their physical lengths may be as short as pally by thateld which gives rise to apcurrent Itending to ilow across its long dimension and no other, the slots are preferably made very thin. For example, when the operating frequency band lies between the guide wavelength limits of 3.1 to^3.5v centimeters, that is, the band for which a one inch by 1/2 inch rectangular waveguide is best suited for carrying power in the TEo,1 mode,

Y,the slots 2I of coupler A may each be 0.496i0-002 inch long and 0.156 inch thick. Two longitudinal rows'of five slots 2l each,fwith about 0.040 inch between the ends'of adjacent slots in each row, then provide a suitable hybrid. In couplers B and C, the transverse slots 22. may at the same ft'imev be 0270x0001 inch long by 0.063i0-001 inch wide, and the longitudinal slots 23 may be 0144010001 inch long by 0.125i0.001 inch wide.

A single row of eighteen transverse'slots 22,

' evenly spaced about 0.120 inch apart between centers, and four rows of iive longitudinal slots '23 each provide a suitable hybrid. The longitudinal slot rows are in pairs, one pair on each side of the centrally located row of transverse slots 22. For convenience in cutting them, the

longitudinal slots of each pair of longitudinal y slot rows are half-staggered from one row to the next, and the longitudinal spacing between the centers of a slot in one such row and a next successive slotV in the other such row is conveniently about 0.240 inch. The spacing between two such rows may be about 0.040 inch. The

4 slots 2I of coupler A are also staggered, in this case to attain optimum directivity.

As developed in the aforementioned copending application, the spacing between slots in couplers like B and C has little or no effect on the coupling ratio, but there is an improvement in directivity when the spacing is reduced. The coupling ratio is determined by the nature of the individual slots and the number of slots employed in each coupler.

In operation, input signal voltages are introduced into the iirst, third and fourth waveguides II, I3 and I4, respectively, at input terminals I I, 1 3 and 1 4, respectively, and output voltages are taken from the four waveguides II, I2, I3 and I4 at output terminals O I, 0 2, 0 3 and 0 4, respectively, the last of which is not shown in the drawings, but is directly beneath terminal O I. The input end 1 2 of the second waveguide I2 is closed with -a termination plate 25, which may conveniently be provided with a wedge-shaped piece of wave-absorbent material 26 mounted on the inner side of the plate, with the vertex directly inwardly along the axis of the waveguide. The material 26 may be hardwood or Bakelite coated with colloidal graphite, known as Aquadag, for example, and provides a non-reflective termination that i5 not sensitive to frequency changes.

The local oscillator signal is introduced at terminal I I from the local oscillator 24. It is de sired that this signal shall be divided into four substantially equal parts which become available in all four waveguides, and accordingly one coupler, A, is placed closer to the input end of the circuit than the other couplers, B and C. As shown in Fig. 5, the local oscillator voltage encounters coupler A rst, where it is substantially evenly divided between the rst and second waveguides I I and I2. In the rst waveguide II, one half of the local oscillator power then encounters couplerB, where it is substantially evenly divided into quarter portions between the first and fourth waveguides II and I4, respectively. In the second waveguide I2, the other half of the local oscillator power then encounters coupler C, where it is substantially evenly divided, again into quarter portions, between the second and third waveguides I2 and I3, respectively.

The received signal, which in the usual radar system is available from the antenna 21 by way of the duplexer or T R circuit 28, is introduced at terminal 1 4, and in the fourth waveguide I4 it encounters coupler B, where it is substantially evenly divided into signals of equal power between the first and fourth waveguides II and I4, respectively. The A. F. C. voltage from the transmitter 29 is introduced at terminal 1 3 through an attenuator 30, for only a sample of the transmitted power is desired, and in the third waveguide I3, this power encounters coupler C, where it is substantially evenly divided into signals of equal power between the second and third waveguides I2 and I3, respectively.

Thus, there are available, at each of terminals O I and 0 4, both the local oscillator and received signal voltages, with equal power at each terminal; and at each of terminals 0 2 and 0 3, there are both the local oscillator and A. F. C. voltages, with equal power at each terminal. The respective power divisions having been accomplished by means of directional couplers, substantially none Yof the input power from any of the sources is reflected back to the input terminals. The sources of the signals that are :oscillator and -receivedwsignal voltages have no particular `phase relation, however. In fact, the local oscillator frequency is higher or lower than that of the received signal frequency by lan amount which is intended to be equal to the intermediate frequency. Figs. 9A and 9Biil1us- Atrate the situation with respect to these two voltages at the two output terminals O-'-I andl`O.-4,

respectively. Local oscillator vector 38 in Fig. 9B lags 90 :degrees behind local Voscillatorfvectorf31 in Fig. 9A, while received signal vector 4I Fig.

9A lags 90 degrees behind received signal vector inA Fig. 9B. The local oscillator vectors 31 and '38 are equal to each other in magnitude, and the received signal vectors 40 andA 4I are equal-.to feach other in magnitude, but the latter two vectorsgarenoty necessarily equal to the former-two inmagnitude. Actually the signal voltage -is ordinarilyfvastly weaker than the local oscillator V=.fvoltage. The phase relation between vectors-31 and 40, corresponding to the signals directly connectedto the input terminals I--I and I-4, re

'spectively,- has been chosen at random.

The voltages'that are presented'to amplifier input-terminals 54 and 55 (in Fig. 5)v after detection of the signals from the two outputterm-inals arethe modulation'envelopes generatedwhen the local oscillator signal modulates the received signal, orvice versa. oscillator voltage is of` a higher frequency than ",the received signal voltage, this situation can be v illustrated vectorially by rotating the local oscillator vectors 31 and 38 'at a constantY rotational speed-and by same amount lwith respect to the Assuming that the local received signal vectors 4I and 40, respectively.

-The direction is arbitrary, and in Figs. 10A and 10B,'ve :tor` 31 has been rotatedclockwise until it is oppositely phased to vector 4I, whereupon it is evident that vector 38, when rotated by the same amount and in the same direction with respect to vector 40, is in phase with vector'40. At this instant, the modulation envelope ofthe voltages from terminal O-I has reached a minimum value, while that of the voltages from ter- .minal O-4 has reached a maximum value. Re-

ferring now to Fig. 11, two modulation envelopes are there illustrated, that at A corresponding to the envelope generated by the vectors in Fig. 10A, and present in the mixer 52 connected to terminal O--I, and that at B corresponding to the envelope generated by the vectors in Fig. 10B land present in the mixer I connected to terminal O--4. Fig. 10 illustrates the instantaneous vector relations at time t1 in Fig. 11. Continued rotation'v of 'vectors 31 and 38 in a clockwise. di-l rection until vector 31 is in phase with vectorlll kwill bring vector 38 into phase opposition with vector 40. velope A'becoming a maximum and modulation This will 'result in modulation "enenvelope B becoming a minimumyat time t2 in Fig.` 11. The distance from a maximum to Va minimum in a modulation envelope is 180 electri- -cal degrees,as is apparent from Fig. 1l, so that the by 180 degrees. Considering now the voltages introduced into thel input ends of the waveguides, and specifically the local oscillator voltage which is incident upon terminal I-I', there is usually present one or more additional voltages in the nature of noise of a different frequency or frequencies and of low` amplitude. Considerfor example, a noise signal of higher frequency than `that of the -local oscillator voltage. .At aparticular instant, as shown-in'Fig. 12A, the `local oscillator voltage, represented again by vector 31, is` at the output of the first waveguide -II. A noise voltage at the output of the samel Waveguide isrepresented by vector 61. Some time later the noise, being of higher frequency, will have advanced in phase with respect to the main local oscillator voltage by some angle a, so that f vector v61 will have assumed a new relative position Vwith respect to vector 31, as indicated by the dotted line vector 61". In passing through the coupler into the waveguide I4, both the main and noise voltages vare delayed by the same amount, 90 degrees, as indicated by vectors 38 and 68 representing the condition at said particular instant. At the same later timep at the output terminal O--4 of the fourth waveguide I4, the noise will have advanced with respect to the main local oscillator voltage by the same angle a as in the rst waveguideV I I, for -the paths are symmetrical, so that vector 6-8 will have advanced with respect to vector 384 by the angle a to a new position as indicated bythe-dotted lin'e vector 68. The `vectors in Fig. 12B are thus in the same relative position as Vthe vectors in Fig. 12A at all times; The modulation envelope generated when vector B1 modulates vector 31 is then maximum and minimum at the same times as that generated when vector 68 modulates vector 38, so that, at thev output terminals, the two modulation envelopes, due to noise introduced into any one input terminal along with the desired input signal, are in the same phase. When the mixers f 5I and 52 are connected to a'push-pull amplifier Referring now to Fig. 13, the output terminalsv O-I and O-4 of the rst and fourth waveguides II and I4, respectively, 'are shown. Crystal mixers or detectors 69 and 62 are in the output circuits-of terminals 0 4 and O-I, respectively, in place of the block diagram mixers 5I and 52, respectively, of Fig.,5. y T he free ends of the two waveguides beyond the mixers may ybe terminated by any. suitable reactive termination, such asa suitably placed short circuit 12, as is known in the art. The amplierA 53 includes an input transformer 63 and a first amplifier tube 64. The primary winding 65 of the transformer is connected at each of its ends 54 and 55 to one of the crystals 62 or 69, respectively. The transformer terminals 54 and 55 are the input terminals of the amplifier 53. The center point 66 of the primary winding 65 is connected to the metal of the waveguides Il and I4 by way of ground connections 10, 1I. The crystals 68 and 62 are connected to the primary winding 65 in opposite sense. Consequently, the direct current .that flows in the .lower crystal vin Fig.

13` -flows -throughthe--crystalground at ln and- 1I, downwardthroughnthe' lower half. of thei primary", winding-5.6 5,-. as-.shownf bythe lower arrow and hackv to f the lowers crystal. Simultaneously;` the .direct-'current that: flows through,

thegupper crystal B2` flows through ground-at lil andi'll and thence-fupwardthrough thevupper half. of the primarywinding 65;.as shown by the Y upper arrow; and back to theupper crystalf.

The two D. C. components are. insense opposition in the primary winding. 65-.and hence v'have no effect onthe remainder -of the lampliiiercircuit.

The modulaticnenvelopesA and Bfof Fig. 11-r are detected bythefcrystals` and-:become sinusoidalvariations. on therD. C. which aree180 degrees out of phase witheach other.. Hence', the crystals :being connected tothe primary winding 65;

in opposite sense',.duringione.half ofthe alter nating currentY cycle theref-is an increase in the current that flows upwardin the fupper halfof the primary windingf anda-simultaneous decreaseY in the currentthat ows in the Vlower4 half. thereof; andnduringg the other; half cyclethere is an increasein' the current that ows voltagafashascbeeniset Vforth above, thesezxappear-in the sameI phase in-rthetwooutput terminals. Hence `the :currents that flow in the two halves'fof the aprimarywinding aspa result ofdetection of these Venvelopes :cancelfeachother as= faras the -fsecondarywinding is'.y concerned.

It is now cleanthatthe.invention provides a mixer circuit for v.electric waveswhich; of itsv own nature, provides an vimproved :signal .to noise' ratio. The;circuitf` iszmechanicallysmall andA compact, .unlike -the f soz-called magic-Tee and' Rat Race arrangements;` whioh'are characten-e izedby a rectangular joint of one :waveguide with:` another and elongatedr arms 4for Vrmttching and iV phasing purposes; Thewpresent inventionfmakes convenient use :of f thefffaet :that-f a -symmetrical quadrature directional coupler hybrid permits' waveguides to'loewoupledF together While Vin 4a The compact mutually parallely` relation at the saine time with all. the desired.. electrical advantages of improving the fsignaltownoise ratio by providing the desired and. undesired voltagesv in cliffV ferent. characteristic phasezrelation, .so that one'- rnay be separated from the other.

Thesecondand third waveguides; l2 f and I3 and coupler C are `identical from an analytical point of view to the .first and fourthv waveguides Il Vand I4 and their coupler` B. The local os cillator` signal is introducedinto .the second Wave- Y guide...|2 byy way. ofcoupler Arbutit is presented toQthe output terminals.. O-2 and. 0 3 in the.

samemanner andfashion as..tooutput terminals. OY-I and O.-4.. The A; F. C..voltage is operated upon. in: thesame .manner .as the received. signal,. sog-. thatthe entire-foregoinganalysis applies with equal force. tothe. situation at. output terminals Many modifications of the invention will occur.:

tosthose skilled .inthe .ar-t.-` Foi-.s example, .various other typespfdirectnal couplers` can be usedV inthe. invention-at the optionv of.` the user. TheY .tions lustrated. "Variousotherarrangernents. are .pos-t v Sibley-such as a .flat .arrangement, wherein .all .the..j waveguides are coupled through narrow. walls,...

or la A.vertical arrangement; wherein all.. coupling... is .through widawaus.oayariatons-oflbothzof.. these. The embodiment ;illustrated..-is..valuable forits compactnessgbut-t will be..realizedlthat'l the inventionincludesjany.mechanicalarrangement which.providesfthefelectrical circuit.- shown. in ylig;i 5. It should be understood. that,.althoughl the-drawingsnillustratetwo :balanced mixers, .each of,.these is .anembodiment ofthe-.invention in... itself. p It,- is, .therefore, intended. that-the. claims. that f ollow shallnotbenlimitedz tov` particular. de-VEL tails-,of--the embodimentinthe-.invention`v herein illustrated, but shall be limited only by the prior.;n art..

1. A: transmissondirle;L circuit for-mixing v,pounirr at one .frequency.,individua1ly g-w itl1,..each.7 of;` two c. signals :leach .atf a frequency different from.A saidl. one,frequencypcomprisingc rst,second;.thirdandt. fourth transmissionline vsectionsVeach-.having an?. input end and-.an output. end; first symmetrical-,` directional. coupler.:meansfbetween saidl first .fand-l. seconda sections second-Y symmetrical.` directionali couplenmeans 'between.saidirst'andv fo.urth.sec.

thirds` symmetrs'l'ca-l=` directional. coupler. meanssbetween -saidzsecond f and -third,sectionsf; said flrsti coupler being.` nearer-.tothe inputv end of.. said inist; section. vthan said-.second'couplerf and. nearer to the input end offsaidsecond:section-.fl

y thanf said:thirdicoupler.;.r andfanindividual .mixer means connecte'clcto :'theaoutput` endfof each l.sec-ftion.V

2. A1transmission?linef'circuitY for. mixing power. at ione frequencyfzindividuallywith each off.two.- signals .leachfiatra .freq'uencyfdifferent:from1salda` one. frequency. comprising: rstf. second,.. ,third-.= and` 'fourth'.transmissionfline sections; each have; ingan input end-andk an-.routput /rend first. sym-fi metrical: directional coupler-:means `between said-.r rstrandsecond sections second symmetricalfdif.-r rectional: coupler: means- :between said first' f andaV fourth sections ;r thirdzsymmetrical. -.directional: coupler` meansibetween said=secondandfthirdsec#y f tions; said' first :coupler :being .fnearerpto the finput. I, end ofsaidlfirst:sectionzthanpsaid.secondtcouplerfl and nearer-to the input ven'clzofel saidzsecond sec@ tion than said third coupler; a substantially noneV reflective termination irif the 'input vendaof lsairl second. section; and...an.'individua-l mixerfmeansc connected'- lto. .the output 'endf of.y each sections.`

3. A transmissiondinecircuit fonmixing power:v at one frequency'withfeachfof twovsig-nals havingcf. frequencies, different front,saideonefffrequency1v comprising:- firstisecondfthird andv fourth transsy mission:` line sections, ,eachfhavi-ngc; an? input end andan output. end first'. symmetrical directional,... couplerz'means between: saidrfirst.andlsecondsea f, tions secondi syrnmetricah directionale.. coupler. means- .f betWeeni-:said-.iirsta and. fourth. sections;l third- ,symmetrical directionak coupler meansfbe'-, K tween said .secondand-.third sections;.- said..cou. plers eachhavingsubstantially alone-.torchecoi-` plinggratio ;1said.flrst coupler being nearer to' th'e'j.V input end..of..said firstV section..thansadecond coupler and nearer" t the input end 'of "said sec?l ondsectionthansaidthird coupler; and .an individual Vmixerfmeans ,connected to the outputl 'end of each section...`

4.. A. transmission. lie -circuit. for .mizi'rg power abone frequency withleacli .of'two' signals.haviz'igi,v

gassoso frequencies different from said one-frequency coupler means between said first and second sections; second symmetrical directional coupler means between said first and fourth sections; third symmetrical directional coupler means between said second and third sections; said couplers each having substantially a one-to-one coupling ratio; said first coupler being nearer to the input end of said first section than said second coupler and nearer to the input end of said second section than said third coupler; a substantially non-reflective termination in the input end of Vsaid second section; and an individual mixer means connectedvto the output end of each section. f Y

5. A waveguide circuit for mixing power at one frequency with each of two signals having frequencies different from saidY onefrequency comprisingriirsasecond, third and fourth waveguide sections, each having an input end andan output end; first symmetrical directional coupler means between said first and second sections; second symmetrical directional coupler means between said first and fourth sections; third symmetrical directional coupler means between said second and third sections; said first coupler being nearer to the input-end of said first section than said second coupler and nearer to the input end of said second section than said third-coupler; and an individual mixer means connected to the output end of each section.

6. A waveguide circuit for mixing power at one frequency with` each of two signals having frequencies different from said one frequency comprising: first, second, third and fourth waveguide sections, each having an input end and an output end; rst symmetrical directional coupler means between said first and second sections; second symmetrical directional coupler means between said first and fourth sections; third symmetrical directionalfcoupler means betweensaid second and third sections; said first coupler being nearer to the input end of said first section than said second coupler and nearer to the input end of said second section than said third coupler; a substantially non-reflective termination in the input end of said second section; and an individual r mixer means connected to the output end of each section.

'1. A waveguide circuit for mixing power at one Y frequency with each of two signals having fre-V quencies different from said one frequency comprising: first, second, third andfourth waveguide sections, each having an input end and an output end; first symmetrical directional coupler means between said first and second sections; second symmetrical directional coupler means between said first and fourth sections; third symmetrical directional coupler means between said second and third sections; said couplers each having substantially a one-to-one coupling ratio; said first coupler being nearer to the input end of said first section than said second coupler and nearer` to the input end of said second section than said'third coupler; and an individual mixer @sans connected to the output end of each sec- 8. A waveguide circuit for mixing power at one frequency with each of two signals having frequencies different from saidone frequency comprising: first, second, third, and fourth waveguide sections, each'having an input end and an output end; a substantiallynon-reflective termination in the input end of said second section; first symmetrical directional coupler means between said first and second sections; second symmetrical directional coupler means between said first and fourth sections; third symmetrical directional coupler means between second andA .j

third sections; said couplers each having substantially a one-to-one coupling ratio; said first coupler being nearer to the input end of said first section than said second coupler and nearer to the input end of saidv second section thansaid third coupler; and an individual mixer means connected to the output end of each section.

9. A waveguide circuit for mixing power at one frequency with each of two signals having fre-v i quencies different from said one frequency comprising: first, second, third and fourth waveguide sections, each having an input end and an output end; a first common wall between said first and second sections, and first symmetrical directional coupler means therein; a second common wall between said first and fourth sections, and second symmetrical directional coupler f means therein; a third common wall between said second and third sections, and third symmetrical directional coupler means therein; said Y first coupler being nearer to the input end of said first section than said second coupler and nearer to the input end of said second section than said put end and an output end; a common narrow wall between said first and second sections, and first symmetrical directional coupler means therein; a common wide wall between said first and fourth sections, and second symmetrical directional coupler means therein; a common wide wall between said second and third sections and third symmetrical directional coupler means therein; said first coupler being nearer to the input end of said first section than said second coupler and nearer to the input end of said second section than said third coupler; and an individual mixer means connected to the output end of each section.

11. A waveguide circuit for mixing power of one frequency with each of two signals havingv directional coupler means therein; a common wide wall between said second and third sections and third symmetrical directional coupler means therein; said first coupler Vbeing nearer tothe input end of said first section than said secondl coupler and nearer to the input end of said sec- 7 ond section than said third coupler; a substantially non-reflective termination in the input end of said second section, and an individual mixer end of each secmeans connected to the output tion. Y*

12. A waveguide circuit for mixing power at oneV frequency with each of two signals having frequencies different from said one'frequency comprising; first, second, third and fourth rectangular waveguide sections, each having an input end and an output end; a common narrow wall between said first and second sections and first symmetrical directional coupler means therein; a common wide wall between said first and fourth sections, and second symmetrical directional coupler means therein; a common wide wall between said second and third sections, and third symmetrical directional coupler means therein; said couplers each having substantially a one-toone coupling ratio; said rst coupler being nearer to the input end of said first section than said second coupler and nearer to the input end of said second section than said third coupler; and an individual mixer means connected to the output end of each section.

13. A waveguide circuit for mixing power at one frequency with each of two signals having frequencies different from said one frequency comprising: first, second, third and fourth rectangular waveguide sections, each having an input end and an output end; a common narrow Wall between said rst and second sections and first symmetrical directional coupler means therein; a common wide wall between said rst and fourth sections, and second symmetrical directional coupler means therein; a common wide wall between said second and third sections, and third symmetrical directional coupler means therein; said couplers each having substantially a one-to-one coupling ratio; said first coupler being nearer to the input end of said first section than said second coupler and nearer to the input end of said second section than said third coupler, a substantially non-reflective termination in the input end of said second section, and an individual mixer means connected to the output end of each section.

14. A transmission line circuit for mixing power at one frequency individually with each of two signals each at a frequency different from said one frequency comprising: first, second, third and fourth transmission line sections, each having an input end and an output end; first symmetrical directional coupler means between said first and second sections; second symmetrical directional coupler means between said rst and fourth sections; third symmetrical directional coupler means between said second and third sections; said rst coupler being nearer to the input end of said rst section than said second coupler and nearer to the input end of said second section than said third coupler; first, second, third, and fourth means for detecting difference frequencies connected to the output ends of said first, second, third and fourth sections, respectively; first push-pull amplifier means connected to the outputs of said first and fourth detecting means for amplifying the difference frequency of frequencies introduced at the input ends of said first and fourth sections; and second push-pull amplier means connected to the outputs of said second and third detecting means for amplifying the difference frequency of frequencies introduced at the input ends of said first and third sections.

15. A transmission line circuit for mixing power at one frequency individually with each of two signals each at a frequency different from said one frequency comprising: rst, second. third, and fourth transmission line sections, each having an input end and an output end; rst symmetrical directional coupler means between said first and second sections; second symmetrical directional coupler means between said first and fourth sections; third symmetrical directional coupler means between said second and third sections; said first coupler being nearer to the input end of said rst section than said second coupler and nearer to the input end of said second section than said third coupler; first, second, third and fourth means for detecting difference frequencies connected to the output ends of said rst, second, third and fourth seotions, respectively; first push-pull amplifier means connected to the outputs of said first and fourth detecting means for amplifying the difference frequency of frequencies introduced at the input ends of said first and fourth sections; second push-pull amplifier means connected to the outputs of said second and third detecting means for amplifying the difference frequency of frequencies introduced at the input ends of said first and third sections; and a substantially nonreflective termination in the input end of said second section.

HENRY J. RIBLET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,059,601 Peterson et al. Nov. 3, 1936 2,382,693 Dallenbach et al. Aug. 14, 1945 2,410,387 Mueller Oct. 29, 1946 2,462,893 Pontecorvo Mar. 1, 1949 2,468,166 Bruck Apr. 26, 1949 2,468,237 Sanders Apr. 26, 1949 OTHER REFERENCES A New Type of Waveguide Directional Coupler, Proc. Institute of Radio Engineers, January 1948.

Directal Couplers, Proc. Institute of Radio Engineers, February 1947.

A Mathematical Theory of Directional Couplers, Proc. IRE, November 1947. 

